Moscow says it will 'target' US coalition aircraft in the west of Syria's Euphrates River after US downed a Syrian jet.

Russia has said that it will treat all US-led coalition aircraft to the west of the Euphrates River in Syria as "targets" and halted an incident-prevention hotline with Washington after US forces downed a Syrian warplane.

Moscow has only once before suspended the hotline, which was established in October 2015 to prevent conflict between the different forces operating in Syrian airspace.

Sunday’s downing of the jet and Russia's response on Monday further complicates Syria's six-year war and come as the US-led coalition and allied fighters battle to remove the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group from its Syrian bastion, Raqqa.

Russia's foreign ministry accused Washington of failing to use the hotline before downing the plane near Raqqa and called for a "careful investigation by the US command" into the incident.

"Any flying objects, including planes and drones of the international coalition, discovered west of the Euphrates River will be tracked as aerial targets by Russia's air defences on and above ground," it warned.

Russia's defence ministry condemned the downing of the jet in a separate statement, saying the latest incident, in addition to others, was a violation of international law.

"As a result of the strike, the Syrian plane was destroyed. The Syrian pilot catapulted into an area controlled by Islamic State [of Iraq and the Levant] terrorists. His fate is unknown," the statement said.

'Not much change on ground'

Pavel Felgenhauer, a military analyst and columnist in Moscow, said that the development was a dangerous escalation, but the sides did not want to take real action against each other.

"Russia's defence ministry does not say that they would target American planes with weapons. Moscow says they will just lock their radars on them, follow them but not really shoot," he said.

Felgenhauer added that this happened various times before the latest incident when US planes came close to Russian bases in Syria.

The Syrian jet was shot down on Sunday evening after regime forces engaged fighters from the Syrian Democratic Forces (SDF), an alliance battling against ISIL with US support, in an area close to Raqqa.

The American F/A-18E Super Hornet shot down the Syrian SU-22 around 7pm as it "dropped bombs near SDF fighters" south of the town of Tabqa, the coalition said in a statement.

The incident was the latest skirmish between the US-led coalition and regime forces in the increasingly tense and crowded space in Syria's north and east.